**3.1. Determining if exposure has occurred**

Once a skin biopsy was collected from a free ranging whale the skin was used to measure the levels of chromium present. The different valence states of chromium cannot accurately be determined, so we measured the total level of chromium in the tissue (Figure 1). For North Atlantic right whales in the Bay of Fundy, 7 biopsies were collected. The total chromium levels in right whale skin (wet weight) ranged from 4.9 to 10 ug Cr/g tissue with an average of 7.0 ug Cr/g tissue. (Figure 1A). For sperm whales, 331 biopsies were collected from 17 different regions around the globe. In sperm whales, the total chromium ranged from 0.9 to 122.6 ug Cr/g tissue with an average of 9.3 ug/g w.w (Figure 1B). The highest mean levels by region were found in the Bahamas with an average of 81.9 ug/g w.w for 2 animals. The average was slightly higher in sperm whale tissues than North Atlantic right whale tissues (Figure 1C).
